1. Field of the Invention
The present invention generally relates to depth gauges and measuring devices and more particularly to a device for measuring the depth of concrete decks, roads, streets, highways, and related structures.
2. Description of Related Art
Most modern bridges and similar structures are constructed by pouring a concrete deck over a matrix of beams. Once the beams matrix is placed, forms or molds are connected to the beams to provide support for the plastic concrete as it is poured and finished in accordance with a predetermined construction plan or blueprint. Typically, two layers or grids of tied rebar are placed on top of the beams before the concrete is poured. The rebar provides internal structural support for the eventual concrete slabs that will be formed. As is well known in the art, the process of pouring, consolidating, and finishing the concrete is a very fast paced operation usually occurring at night under severe time constraints dictated by the necessity for ingress/egress over the particular structure being built, repaired, or refinished.
In order to provide an acceptable deck within the timeframe that modern contractors are expected to work, mechanical screeds are used to finish the surface. These large truss-like machines ride on rails parallel to the deck being poured and, as the concrete is placed, the screed passes over the plastic concrete. Beneath the screed is a pair of rollers that are moved rapidly from one side of the screed to the other, smoothing the surface of the concrete. The operation of the screed is almost entirely automated.
Despite the rapid pace and stringent time constraints, concrete bridge decks are expected to be constructed in accordance with a set plan or blueprint and deviation from the plan can lead to increased costs due to repair, restoration, or complete reconstruction. Accordingly, as the screed progresses along the deck of the bridge, the total thickness of the deck and the depth of the layer concrete over the top grid of rebar (i.e. cover) is measured at random locations, usually by an onsite construction engineering inspector (CEI). Many times, the contractors have their own quality control (QC) representative on site to take these measurements as well.
Traditionally, a CEI or QC representative will employ a rudimentary depth-measuring device such as a simple stiff wire, dowel, or the like. The inspector typically inserts such a wire or dowel into the concrete, removes it, and then measures the length of cement paste left on the wire/dowel with a tape measure. In addition to using such a stiff wire or dowel to determine the total depth, a metal plate is often used to measure depth of the concrete cover over the top grid of rebar. If shallow spots are discovered, either with respect to total depth or the rebar cover, the screed must be adjusted in order to minimize the deficiencies and assure that the rest of the deck is placed correctly.
There are a few problems and disadvantages that are apparent when the stiff wire or dowel rod method of inspection is used. First, the inspector is often charged with creating his own tool, be it a stiff wire, straightened coat hanger, or dowel. At first thought, one might find these simple devices so readily available that this would hardly seem a problem; however, plastic concrete is not that soft of a material so a typical wire, coat hanger, rod, or dowel can easily deflect and/or be deformed by the coarse aggregate, particularly over a series of measurements. While a dowel rod might be somewhat larger and less prone to deflection or deformity, the bottom end can often times hit a coarse aggregate squarely, giving the inspector the false impression that the deck is not thick enough in that particular location.
In addition to the problems encountered while measuring the total thickness of the deck, the inspector must also measure the depth of the concrete cover over the rebar. This is typically accomplished with a tool, also of the inspector's fabrication, that must be large enough to span the largest spacing in the rebar grid, typically 12 inches (but the desired width may vary depending on the concrete application). Some inspectors employ a carpenter's square, L-shaped ruler, or rebar with an L-shaped bend. Accordingly, in order to measure both the depth of the cover and the total depth of the concrete, the inspector necessarily must fabricate, carry, and subsequently carry out measurements with two tools. With this equipment, inspectors must, at every point, insert the wire into the plastic concrete to the full depth, extract the wire, and then measure the smear of cement paste on the wire with a tape measure. The process must then be repeated with the L-shaped bar in order to measure the cover depth. Both readings must be taken behind the rollers of the screed (a safer method that results in footprints in the finished concrete) or just in front of the rollers (a method that leaves no signs of testing in the final concrete but only allows several seconds to measure before the rollers make another pass) while the concrete forming process is being carried out. The time constraints and cumbersome nature of employing two tools and a tape measure eventually leads to hasty and inaccurate depth measurement. Accordingly, there is a clear need for an improved depth measurement tool that allows the inspector to easily measure both the total concrete depth as well as the cover depth without the need for multiple tools or external measuring devices, such as a tape measure.
Several attempts at providing such an improved tool have been made, however none have sufficiently solved the problems outlined above. For example, U.S. Pat. No. 7,735,232 to Bahler, describes paver or brick bed shaping tool incorporating a depth measuring gauge. This device includes a guide member, screed member, and adjustable hardware for assembling them for relative movement between the major components. This device is used to shape a paver or brick bed under layer as well as measure depth, and provides for adjustability. The guide member has a pair of extension arms protruding laterally from the device at two different, fixed heights for measuring the differing depth of deck layers, for example sand, base materials, pavers or the like. The screed member is dragged across the base paving layer perpendicular to the surface in order to shape the layer. Accordingly, this device can measure and shape and control the depth of both a base layer and an overlying upper layer which are used in preparation of a bed for installation of additional materials.
U.S. Pat. No. 6,298,547 to Baker illustrates a bituminous paving depth gauge, used to measure a hot bituminous pavement layer before compaction to determine proper material depths. The mechanical device includes a top reading paving depth gauge to determine the thickness of the paving layers. The gauge includes a depressible rod operatively associated with a structural rod support system. The rod has a bottom portion that is slidably mounted within the rod support. The upper section includes a graduated measuring gauge fixed on the rod support system. The lower section has a bottom support device fixed to this end of the rod support system, and acts as a “foot” for the measuring gauge. Accordingly, while providing a general depth gauge, the device in Baker fails to provide a means to measure a concrete cover layer which may be disposed above a grid of rebar or other support structure having interstitial spacing. Additionally, the foot of the device in Baker will not provide a stable base for measuring depths of concrete below the rebar grid.
U.S. Pat. 3,460,260 to Sarlandt relates to a grade setter for determining variations in grade levels for example in roads, streets or highway construction. An example is given of a completed paved highway as normally requiring three (3) levels which must be determined, for example a base level above the soil, the level of the concrete above the level of aligned treated base, as well as an additional level of pavement above that of the concrete. This device includes markers at selectable levels along a rod which has oppositely progressing scales with a common zero at predetermined distance above the rod. A slide mounts a horizontal telescope which has on one face a scale progressing downwardly and on another face a scale progressing upwardly from a lower telescope holder. The separate faces carry cursor for correlating the slide scale with the adjacent rod scale which is seen through a window. The device is plunged into a base layer on top of a hub having a stake of a known depth until the device makes contact with the top edge of the hub, then a measurement can be taken. The measurement is relative to the hub stake depth. Sarlandt does not provide a measure to measure a depth of concrete below a supporting rebar grid nor does it provide a blade for measuring the cover above the rebar.
It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed. However, in view of the concrete depth measurement devices in existence at the time of the present invention, it was not obvious to those persons of ordinary skill in the pertinent art as to how the identified needs could be fulfilled in an advantageous manner.